Data Supplement

Figure S1. and S2. Table S2. and S3.
-
Breeding and wintering ranges (hatched) for two species pairs included in the present
study, including (a) a pair that does not form a migratory divide (Catharus minimus
[Gray-cheeked thrush, yellow] and Catharus fuscescens [Veery, blue]) and (b) a pair
that does form a migratory divide (Geothlypis tolmiei [MacGillivray’s warbler, orange]
and Geothlypis philadelphia [Mourning warbler, purple]). Green shows the overlap between
ranges in (a). Modelled relationship between overall phenotypic divergence and three
additional predictor variables included in the final, averaged linear mixed effect
model. Migration category was also included (relationship shown in Figure 1) and a
random variable of genus nested within family to control for phylogenetic relationships.
The effect of each predictor is plotted with these additional variables held at their
medians. Results from Brownian Motion and Ornstein-Ulhenbeck (OU) models of evolutionary
change run as described in Table 2a but correcting for slower divergence times using
COI (estimates of p-distance from COI are on average 7.8% smaller than estimates from
cytochrome b). Divergence times for nine pairs were estimated with COI and 37 with
cytochrome b. Divergence times for the remaining three pairs were estimated with the
control region and NADH and were dropped from this analysis.

Article Figures & Data

Figures

Modelled relationship between overall phenotypic divergence and migration category (no divide, divide). Model averaging with linear mixed effects models were run with a random variable of genus nested within family to control for phylogenetic relationships. Significant predictors in the final model included migration category, time since divergence, and body mass. The effect of migration category is plotted with these additional variables held at their medians. (Online version in colour.)

Relationship between phenotypic divergence and time since divergence. Results are shown for all traits combined (a) and each set of traits separately (b–d). Time since divergence was measured using genetic distance; phenotypic divergence was measured using average Hedges' g. Curves show results from OU (Ornstein–Uhlenbeck) models of evolutionary change, fitting separate models for taxa that do (dotted line and open points) and do not (black line and filled points) form migratory divides.

Tables

Results from averaged linear mixed models examining the relationship between phenotypic divergence and a series of predictor variables, including migration category (divide or no divide). Models were run with family and genus as nested random variables and phenotypic divergence as a dependent variable (for all traits combined (a) and each set of traits separately (b–d)). Fixed effects included migration category, time since divergence (p-distance, the proportion of nucleotide sites that differ between clades); geographical overlap, migration distance, breeding latitude, and body mass. Only fixed effects included in the final model are shown; those that are significant predictors of phenotypic divergence (where confidence intervals (CI) do not overlap zero) are shown in bold. Negative parameter estimates for migration category indicate that groups with migratory divides tend to have lower phenotypic divergence than groups without divides. n = number of models in final averaged model (i.e. within ΔAICc of 2), R2 = goodness-of-fit of the global model.

predictor variables

parameter estimates

standard errors

lower CI

Upper CI

(a) overall phenotypic divergence (R2 = 0.56, n = 4)

(intercept)

1.73

1.27

−0.79

4.25

migration category

−0.44

0.11

−0.65

−0.22

time since divergence

0.22

0.047

0.13

0.32

breeding latitude

−0.51

0.35

−1.22

0.20

body mass

0.23

0.098

0.03

0.43

(b) song divergence (R2 = 0.37, n = 6)

(intercept)

−0.0057

1.59

−3.17

3.16

migration category

−0.58

0.17

−0.92

−0.25

time since divergence

0.19

0.073

0.039

0.33

geographical overlap

−0.48

0.55

−1.58

0.62

breeding latitude

0.43

0.53

−0.63

1.50

migration distance

0.30

0.17

−0.036

0.63

(c) colour divergence (R2 = 0.38, n = 9)

(intercept)

1.18

1.69

−2.19

4.55

migration category

−0.45

0.18

−0.81

−0.084

time since divergence

0.24

0.085

0.072

0.41

geographical overlap

1.10

0.61

−0.13

2.32

breeding latitude

−0.52

0.61

−1.75

0.71

body mass

0.30

0.17

−0.041

0.64

(d) morphological divergence (R2 = 0.29, n = 4)

(intercept)

5.28

2.21

0.84

9.72

time since divergence

0.18

0.076

0.028

0.33

geographical overlap

0.71

0.47

−0.23

1.65

breeding latitude

−1.28

0.56

−2.41

0.14

Table 2.

Results from BM (Brownian Motion) and OU (Ornstein–Uhlenbeck) models of evolutionary change. Models including a single evolutionary rate are compared with models fitting separate rates for each migration category (no divide/divide), allowing phenotypic divergence to vary linearly with geographical overlap (overlap) and allowing rates of evolution to vary with both migration category and geographical overlap (no divide/divide and overlap). Models were run with all traits combined (a) and each set of traits separately (b–d). OU models include an additional parameter (α) that constrains the rate (β) of divergence to an intermediate value. β slope describes how the evolutionary rate changes with geographical overlap (α was not permitted to vary with geographical overlap); 95% confidence intervals generated using 10 000 bootstraps are shown in parentheses.